Strange borrowing scope

[Rexagon]

I tried this code:

pub struct Test {
    pub data: Option<u32>,
    pub other_data: u32,
}

impl Test {
    pub fn preload(&mut self) -> &u32 {
        if let Some(data) = &self.data {
            return data;
        }

        // Why `self.data` is still borrowed here?
        // Manually adding scope around `if {}` doesn't help.
        self.data = Some(123);

        &self.other_data
    }
}

I expected to see this happen: it compiles

Instead, this happened:

error[E0506]: cannot assign to `self.data` because it is borrowed
  --> <source>:12:9
   |
7  |     pub fn preload(&mut self) -> &u32 {
   |                    - let's call the lifetime of this reference `'1`
8  |         if let Some(data) = &self.data {
   |                             ---------- borrow of `self.data` occurs here
9  |             return data
   |                    ---- returning this value requires that `self.data` is borrowed for `'1`
...
12 |         self.data = Some(123);
   |         ^^^^^^^^^^^^^^^^^^^^^ assignment to borrowed `self.data` occurs here

error: aborting due to previous error

For more information about this error, try `rustc --explain E0506`.
Compiler returned: 1

Meta

rustc --version --verbose:

rustc 1.60.0 (7737e0b5c 2022-04-04)
binary: rustc
commit-hash: 7737e0b5c4103216d6fd8cf941b7ab9bdbaace7c
commit-date: 2022-04-04
host: x86_64-unknown-linux-gnu
release: 1.60.0
LLVM version: 14.0.0

[Urgau]

It's a limitation of the current borrow checker, using the unstable compiler option -Zpolonius makes the code compiles.

https://rust.godbolt.org/z/PKoaxP3G4

[ehuss]

Thanks for the report! As mentioned, this is a known limitation of the borrow checker. Closing as a duplicate of #54663 (or one of the other issues linked there).